Why is the letter f used instead of s in 18th century English?

You're referring to the common practice in 18th century English of using "f" where we would now use "s" in certain words. This is a result of the historical shift in pronunciation of the letter "s".

Here's a breakdown:

* The "f" sound: In the early modern period (roughly 1500-1700), the letter "s" was often pronounced with a hissing "f" sound, particularly at the beginning of words.

* The "s" sound: Over time, the pronunciation of "s" shifted towards the sharp "s" sound we are familiar with today. This change, known as the Great Vowel Shift, happened gradually and wasn't uniform across the country.

* The "f" vs. "s" conundrum: As the pronunciation changed, the spelling remained the same for a while, leading to words like "fhame" (shame), "fugar" (sugar), "fweet" (sweet), and so on.

* The standardization of spelling: Eventually, the spelling of these words was standardized to reflect the new pronunciation, resulting in the modern "s" sound.

So, the use of "f" instead of "s" in 18th century English is not a random occurrence. It's a reflection of a transitional period in English pronunciation where the letter "s" was still being pronounced with an "f" sound.